This invention relates to a coating apparatus comprising a conveyer belt for objects to be coated, and a pouring head device arranged above the conveyer belt transversely to the direction of movement of the same, for producing a free-falling curtain of poured coating material, as well as lateral curtain-guiding means on either side of the curtain.
A coating apparatus (pouring machine) of this kind has, for instance, been described in European Pat. No. 2040 in connection with the production of solder-stop masks on printed circuit boards.
In these known apparatus, the curtain of coating material descending from a pouring head on to the object or objects to be coated is guided between two lateral curtain edge-guiding means and is thereby stabilized. Experience has shown that the thickness of the poured curtain is considerably larger in the vicinity of these edge-guiding means than in the central region of the curtain. In edgeless coating, i.e., when the entire surface of an object is to be coated, this thickening effect is of no particular importance, as in this case, it is not difficult to choose the width of the curtain to be so large that, in the pouring process, the thicker edge zones will flow down past both sides of the object being coated, and thus will not be deposited on the latter. It is, however, different in those cases in which, for some reason, the marginal zones of the object, opposite one another, are not to be coated so that the width of the curtain being deposited thereon must be less than the width of the object. In these cases, there will be produced, due to the thickened marginal beads of the curtain, correspondingly thickened lateral rims in the resulting coating which, in many cases, are not acceptable on the coated object.